This invention relates generally to positioning a gear member onto a core pin in preparation for molding a plastic drive gear, and particularly to increasing the efficiency of mounting the gear member onto the core pin in preparing the mold for the molding process.
The teeth of certain gears are oriented in one direction so as to provide a biting grip into the driven part. Typically, the driven part is not a gear but a take-up spindle. A particular case is the take-up spindle for a correctable ribbon cassette. A ratchet mechanism of the drive gear is rotated by a mechanism of the printer or typewriter while the used ribbon of the take-up spindle is pressed by biasing means into the gear teeth of the drive gear, thus causing the take-up spindle to rotate and to draw the unused ribbon from the supply spindle. In order to achieve reliable operation, the teeth of the drive gear are both pointed and angled, or tilted, in the direction of rotation so as to achieve maximum bite into the used ribbon around the take-up spindle.
The manufacture of the plastic drive gear is done by molding machine with a hollow metal gear being mounted by hand upon a core pin. The metal gear is stamped in a prior process. The interior rim of the hollow metal gear is configured as is the exterior of the core pin so as to prevent rotation of the metal gear during molding, for example, an octagonal configuration. The hollow metal gear is picked from a tray by hand and oriented by eye and then mounted to the core pin. The cavity of the molding machine is then activated so as to form the drive gear with the plastic embedded around the metal gear. The finished plastic drive gear with its embedded metal gear is then removed from the mold, finally checked for orientation of teeth tilt, and then passed for assembly with the correctable ribbon cassette.
The molding machine used for the process described is generally a vertical machine with the core on the bottom and the cavity on the top with the core pin vertically positioned so that the metal gear does not slide away from its stop in the molding process. Vertical molding machines are by far the least common molding machines as compared to horizontal molding machines and, therefore, are significantly more expensive than horizontal molding machines.
From the above description of the molding procedure, certain problems are apparent. First, the orientation of the metal gear teeth prior to placement on the core pin takes time. Second, it is easy to make a mistake in the placement of the metal gear teeth upon the core pin with the result that the tilt of the gear teeth are oriented in the wrong direction. Third, because the gear teeth are very small, it is difficult to spot every core of incorrect orientation of teeth tilt. Fourth, after the assembly of a drive gear with a cassette with the gear teeth reversed, the only occasion for discovery of the mistake is after purchase of the cassette and installation into a printing machine at which time malfunctioning of the machine will occur. Return of the cassette and discarding of the entire cassette will be the end results.